There are two primary objectives for the glycophorin A-based somatic mutation analysis project. The first objective is to determine the magnitude and types of somatic mutational damage in individuals due to radiation exposure from the Chernobyl nuclear power accident as measured by the glycophorin A (GPA) assay. Analysis will be performed on samples from individuals with both high- and moderate-dose exposures, and will include measurements of the frequency of both hemizygous N0 and homozygous NN variant erythrocytes. Measurements of the frequencies of somatic cell mutations at the GPA locus will be correlated with different indicators of genetic damage from other programs in the program project to provide a comprehensive analysis of genetic damage in these individuals. The second objective is to determine the utility of the GPA assay as a biodosimeter for large population studies of individuals where physical dosimetry information is not available. Measurements of the dose-response relationship, the minimum detectable dose, and the persistence of induced damage will be used to determine the utility of the GPA assay for dose assessment. Results from the GPA assay will be compared with the results from other biodosimeters in the program project to determine the relative sensitivity, cost, and reliability of the different methods.